Art of converting thermal energy into mechanical energy.



ART OF CONVERTING PATENTED JULY 17, 1906.

s. A; REEVE. THERMAL ENERGY INTO MECHANICAL ENERGY. vAPYI-IOATION FILED FEB. 26; 1904.

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-No.'s26,192. PATENTED JULY 17, 1906. .s'. A. RBEVE.

ART OF CONVERTING THERMAL ENERGY INTO ME APPLICATION FILED FEB. 26. 1904.

UHANIUAL ENERGY.

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dium which receives heat energy and by a- UNITED STATES PATENT OEEIoE.

SIDNEY A. REEVE, OF WORCESTER, MASSACHUSETTS. ASSIGNOR TO CHARLES E. BROWN, TRUSTEE, OF READING, MASSACHUSETTS.

Specification of Letters Patent.

ratented July 17, 1906.

Application filed February 26, 1904. Serial No. 195,503.

To all whom, it may concern:

Be it known that I, SIDNEY A. REEVE, of Worcester, in the county of Worcester and State of Massachusetts, have invented certain new and useful Improvements in the Art of Converting Thermal Energy into Mechanical Energy, of which the following is a specification.

In the accompanying specification and drawings I have described my process and illustrated one of the various ways in which it may be practically utilized.

In the accompanying drawings, Figures 1, 2, 3, and 4 are diagrams of different cycles of heat development and expenditure. Fig. 5 shows an apparatus which may be used to embody my process.

The same reference characters indicate the same parts in all the figures.

My invention relates to those processes in which heat-engines of the internal-combus tion type are utilized. By the term internal combustion I intend to include all those devices in which the combustion occurs in a pressure-chamber occupied by the fluid mesubsequent expansion converts a greater or less portion thereof into mechanical energy.

It is Well known that in apparatus of this class the processes just mentioned are 'carried out in a series of steps making up a cyole and that different cycles have been proposed and utilized in practice. In the cycle often designated as the Otto cycle the combustion and expansion both occur in the same engine-cylinder and the combustion is of an explosive nature, which produces a rapid rise both in temperature and pressure of the previously-compressed charge to a point considerably above the temperature and pressure of the charge itself prior to combustion. Since the exhaust-port of the cylinder must open when the piston reaches the end of its power-stroke, the effect of the expansion upon the piston must cease when the gases have expanded to a volume equal to the capacity of the cylinder. Moreover, in most cases this volume of the gases at the instant of exhaust is equal to the original volume of the atmospheric charge before it is compressedthat is to say, a cylinder full of air and fuel is first drawn in and then compressed andafter the combustion is reexpanded to its original volume. This means that there is considerable heat energy which has heretofore been impracticable to utilize in this manner the unconverted heat energy of the exhaust, although various attempts to that end have been made. For example, one method is to arrange a cut-off to take less than a cylinder full of air and gas as a charge to be compressed. Then the subsequent expansion to full-cylinder volume represents an expansion greater than the previous compression. Another expedient is to admit the exhaust into a second cylinder and there permit it to expand against a piston to approximately atmospheric pressure. The first of these two expedients, however, largely offsets the theoretic gain by reason of a lower degree of compression and the smaller capacity of the engine, and in the second expedient the gain is largely offset by loss of heat to the walls of the second cylinder, since the gas (unlike steam) has no store of latent heat to make good the loss in the cylinder-walls without that drop in temperature and pressure, and hence of availability of the heat for work which inevitably accompanies the transfer of the dry ases.

Considering, on the other and, engines working on what is known as the Joule cycle, it will be evident that the situation is different. This cycle may be said toconsist of (a) adiabatic compression to full working pressure, (1)) addition of heat under constant pressure, (0) adiabatic expansion to atmospheric pressure, ((1) abstraction of heat at atmospheric pressure. In this cycle the pressure in the cylinder does not rise above the pressure of the compressed charge, and the heat of combustion (which is a slower non-explosive combustion) is expended about as it is developed in expanding the volume of the charge, but without increasing the pressure, as is the case when the charge explodes in an Otto cycle-engine. Since the Joule cycle cannot be imagined as conducted within a single cylinder performing both compression and expansion, it Will be seen that the charge intake to the compression-department is not of necessity an engine-cylinder full in volume, and hence it peratu-re.

is possible to expand within the engine cylinder or cylinders to atmospheric pressure and to a volume much larger than the original intake volume with consequent superiority in efficiency over the Otto cycle at its latter end.

Engines working on the Joule cycle have hitherto proved impracticable in competition with those of the Otto type, and it is the object of my invention to overcome the defects which have hitherto prevented the profitable employment of the Joule cycle. In

the first place, I have discovered and demonstrated' the theoretical superiority of the Joule cycle over that of the Otto cycle as regards the percentage of applied heat energy returnable in the form of mechanical energy within the same limits of pressure and tei In the second place, I have discovered and demonstrated the reason for the previous inefficiency of engines embodying the Joule cycle, and,in the third place, I have devised means for overcoming the prior limitations in the use of the Joule cycle, which means comprise a series of steps involving modification of the Joule cycle and composing what may be designated for convenience as the Reeve cycle. These three matters will be considered in order.

First. In regard to the theoretical possibilities of the Joule cycle I would refer for a complete analysis of the subject to a work recently published by me, entitled, Thcrm0- dynamics of Heat Engines, New York, 1903. For the purpose of this specification it will be sufficient to make reference to Figs. 1 and 2 of the accompanying drawings, which show, respectively, in diagrammatic form the amount of mechanical energy derivable from a given amount of heat energy in the Otto and Joule cycles, respectively. In these diagrams the ordinates O T represent temperature and the abscissae represent entropy or (loosely and popularly speaking as respects the latter) the heat weight or factor of extent. By the two factors temperature and entropyany given amount of heat en.- ergy may be represented In Fig. 1, illustrating the action of the Otto cycle, O B represent the difference in temperature between absolute zero and the initial tempera ture at which the practical cycle begins. B O represent the increase in temperature due to the compression of the charge. C D represent the rise in temperature and entropy due to the combustion under constant volume, and D E represent the drop in temperature due to the expansion to the original volume of the charge before compression. E B represent the exhaust-line. The area B C D E represents the portion of heat energ i returnable as mechanical work out of the entire amount of heat energy represented by the area O O D 6. Referring next to the Joule cycle in the diagram of Fig. 2, O B represent, as before, the difference of temperature between absolute zero and the initialtemperature of the practical cycle. B C represent the rise of temperature .due to the compression of the charge, which compression, it will be observed, is greater than the compression feasible in the Otto cycle. The line C D represent, as before, the rise of temperature and entropy due to combustion, except that the combustion is now under constant pressure. The coefficient of the abscissa: is there- 'fore greater than that of the curve C D of Fig. 1 by the ratio of the two specific heats for the mixture of gases involved, and the curve C D rises more slowly than C D. D E represent the drop in temperature due to expansion, which in this case is not limited to expansion to the original volume of the non compressed charge, but extends down to atmospheric pressure. The cycle is .then closed by the curve E B, showing abstraction of heat under constant (atmospheric) pressure, whereas the Otto cycle was closed by the steeper curve E B, showing abstraction of heat at constant volume. The area B C D E represents the portion of heat energy returnable in the form of mechanical work, and it is manifestly considerably greater than that of the Otto cycle in Fig. 1. In Fig- 2 the Otto cycle is represented by the dotted lines.

Second. The previous failures in utilizing the Joule cycle have, I apprehend, been wholly or partially due to the failure to recognize the proper relations of the pressures in the two cycles above described. In the Otto cycle the compression of the charge indicated by the line B C of Fig. 1 is limited by reason of the danger of pre-ignition and also by reason of the fact that the subsequent combustion adds an increase of pressure which would become too great if the initial compression were increased. On the other hand, the initial compression in the Joule cycle (indicated by the line B C) represents the maximum pressure of the process, which is not increased by the subsequent combustion. For this reason the initial compression in the Joule cycle may be carried without danger far beyond the initial compression of the Otto cycle and, in fact, if desired, may even be as high as or higher than the maximum pressure of the Otto cycle due to the original compression plus the added pressure of combustion. This shows that a higher degree of initial compression may be availed of to give an area of useful or available heat energy in the Joule cycle, as is indicated in Fig. 2, as compared with Fig. 1. Heretofore this matter has not been understood, and those attempting to utilize the Joule cycle have, so far as I am aware, invariably operated with a compression comparable to that used in the Otto cycle or at least a pressure so low that the available advantages of the Joule cycle were not realized. As a matter of figures, prior experimenters on the Joule cycle have worked at a pressure of one hundred pounds per square inch or less, while I have found that it requires a pressure of at least two hundred and fifty pounds per square inch or thereabout to bring the Joule cycle on a par with the Otto cycle, while for pressures greater than two hundred and fifty pounds there is a decided gain in the Joule cycle over the Otto, wherein the maximum pressures run up as high as .five hundred pounds. In brief, I have discovered that for equal maximum pressures above two hundred and fifty pounds the Joule cycle has a pronounced theoretical advantage. It is an important feature of my process that I produce by the preliminary compression and maintain in the system a pressure at least double that which has heretofore been used with the Joule cycle. experience has led me to adopt a pressure of two hundred to three hundred and fifty pounds as that suitable to secure the results aimed at in my process, since although this cycle does not come on a theoretical par thermodynamically with the Otto cycle until a pressure of approximately two hundred and fifty pounds to the square inch has been attained, yet its mechanical superiority over the Otto engine places it on a competing basis therewith at a pressure slightly below two hundred and fifty pounds. I will designate this as high pressure, and when that term is used herein it will be understood that it means approximately the pressure just mentioned.

Third. In realizing practically the theoretical advantage just mentioned I provide three steps distinguished, respectively, as (a), (b), and (c), which serve in the practical operation of the process, which has as its elementary basis of efficiency the high pressure just mentioned.

(a) I find it essential that the expansion of the fluidv at the described high pressure down to atmospheric pressure, by which the conversion into mechanical energy is accom plished, should be carried out by two or more stages and in two or more cylinders of a suitable motor. This avoids the enormous mechanical strains, cumbersome and expensive construction, thermodynamic losses, and other disadvantages arising from carrying in a single cylinder the large pressure-range which I employ. The first stage will be in a smaller cylinder adapted for high pressure and the second in a larger cylinder adapted for lower pressure. I would here state that it is preferred to so proportion these cylinders that one will be approximately of a capacity to do the work of compression while the other does the external useful work of the motor. I also prefer to perform the preliminary compression in a series of stages. For the former purpose I may utilize an engine constructed like an ordinary compound For convenience steam-engine proportioned as described. This is rendered possible by the means to behereinafter described which serve to overcome the difficulty heretofore experienced with internal-combustion engines in utilizing the exhaust from one cylinder to operate the piston of a second cylinder. For the latter purpose Imay utilize a multistage compressor, which, however, should preferably be directly operated from the pistonrod of the engine with out the intervention of trans1nittingcranks, connecting-rods, gears, or belts.

(b) In the second place, in the internal-con1 bustion type of apparatus herein considered it is needful that the combustion should occur in a dry medium, the ordinary process being the combustion of a fuelsuch as gas, oil, or other hydrocarbonwith a supply of air for affording the oxygen required by the coinbustion. The result of this combustion is the desired amount of heat-energized fluid in the form of gases ready for the delivery or conversion of the energy into mechanical form by their expansion. I/Vith such a medium, however, the multistage expansion heretofore mentioned is not feasible, because, in the first place, it is at too high a temperature to be utilized in an engine-cylinder without abstracting the heat by means of a waterjacket or other expedient, and, in the second place, because the gases when thus robbed of part of their heat are after doing work in the first cylinder possessed of insufficient heat to make good the heat loss due to the abstraction of heat by the walls of the second cylinder without a prohibitive drop in pressure. To overcome this difficulty, I provide for a partial conversion of the heat energy of the gases into heat of steam, thereby reducing the temperature to a point where it is practicable to use the gases in a cylinder, but still retaining the prescribed pressure. By this expedient the second stage of expansion becomes possible, since the steam adds the required latent heat to overcome without substantial loss of pressure the cylinder-wall losses on the entry of the fluid exhausted from the first cylinder into the second cylinder. For this purpose I make use of the apparatus shown and described in my Patents Nos. 588,178 and 588,298, of August 17, 1897, which I will hereinafter consider more in detail. I may add that while this conversion entails a theoretical loss of availability for doing work because of the free fall in temperature from that of the flame to that of the steam there is, on the other hand, a large practical gain arising from the fact that the gases have reached a temperature at which it is rendered unnecessary to water-jacket the cylinders. The pressure is maintained and the heat energy formerly appearing in the temperature of the gases still remains, but now appears in the volume of the steam into which it has been converted.

After the conversion just mentioned of a portion of the heat energy into steam I then superheat (preferably by the same combustion used to give the original heat energy) the steam in the mixture of combustion gases and steam. This gives a second rise in temperature. and the cycle thus produced by the steps just described is indicated in Fig. 3 and for convenience is designated as the Reeve cycle. Here B C represent the rise in temperature due to the compression. Then follows the combustion, Which in the unmodified Joule cycle would raise the temperature along the line C D, Fig. 2, and, in fact, does so in my cycle at the moment of combustion; but by the subsequent conversion into steam the temperature line C D is turned at the point D into a horizontal line, thus representing a constant temperature; but since it does not represent a diminution of the total heat energy it-is extended to the right to D to embrace a heat area comparable to that embraced by the line C D. The rise of temperature by superheating is indicated by the line D D D E represent the drop in temperature due to expansion at constant pressure. EWV B represent the exhaust-line, most of which is horizontal, because the-steam in the exhaust condenses at constant temperature.

W B represent the drop in temperature of the fixed gases after the steam has condensed.

It will be plain from what has been said that the areas, Figs. 1 and 2, described as representing the heat energy theoretically available in the Otto and Joule cycles, involving, as they do, a very high temperature, must be modified in practice. In the Otto cycle the only known practical means for restricting this high temperature is the abstraction and rejection of heat by the water-jacket or its equivalent, and there is available only an area like B C D E in Fig. 1. In the Reeve cycle, however, the high temperature is taken up by the conversion into steam instead of being lost in the waterjacket, and the entire area B C D D D E V is actually returnable in mechanical work. This cycle, therefore, has the capacity of the Joule cycle of increased efficiency by increased pressure, and it has in addition the capacity for making that possible efliciency practically available.

It should be borne in mind that the capability of the mixed working fluid involved in this cycle of being economically adapted to the propulsion of an engine by that method of application which consists in successively expanding the-fluid in a series of stageshas not been demonstrated or practically known prior to my present invention and constitutes one of the elements of my discovery.

Fig. 3 may be considered as representing the temperature entropy diagram for the Reeve cycle as applied to a piston-engine.

When this cycle is applied to a turbine, the elliciency is somewhat higher, owing to the heat.

seeie possibility of going toiahighertemperature.

In Fig. 4 I have compared the temperature entropy diagrams for the pure Joule andthe Reeve cycles as applied to a turbine. B C D E represent the unmodified Joule cycle, and B U D E represent about the proportion of the whole area which wouldbe available in applying this cycle to turbine propulsion, owing to the low maximum temperature whichtheparts of the turbine will stand. The turbine will stand the same temperature for the Reeve cycle-as it will for the dry-gas Joule cycle, and therefore BM N PQR S V IN represent substantially the Reeve cycle as applied to a turbine,this area being obvi-- ously much greater than the area B O .D E. The diagram Fig. 4-may be takenas dem onstrating the impraeticability ofthe dry-gas turbine. I

I have found that in going to the :much

higher compression-pressures necessary in the cycle conducted at the high pressure herein proposed it is desirable-to effect the compression by successive stages. To this end it is permissible to use any suitable form of multistage compressor apparatus whereby the compression may be performed :in two or the gross power developed than with single compression, and at the same time-thereis developed a compressed fluid which canbe introduced into the generator at atemperature (about 380 Fahrenheit) with two-stage compression to two hundred and fifty pounds working pressure) sullicient to materially aid in the complete combustion of dense fluids in a closed combustion-chamber of small capacity andyetnot so high as to effect an undue increase in the temperature of combustionwith its resulting disadvantages. It has been proposed to so compress the working fluid as to introduce it into the combustion-chamber at its maximum temperature with the object of utilizing this temperature to assist combustion and also to conserve the compression For such a purpose a single-stage compressor would be superior to. a compound compressor at the higher pressures proposed by me, because single compression involves. a higher temperature than" compound compression; but I find that it is better to'lose some of the compression temperature and introduce the working fluid into the combustion chamber at a lower temperature than would be normally produced by the single-cylinder compressor, for the sake of mechanical reasons involved in multistage compression and certain other advantages gained thereby, such as a lessening of compressor-conduit radiation losses and favorable combustion-chamber conditions.

Referring to Fig. '5 for a detailed view of 1 0 the apparatus employed to carry out my invention, 10 is the generator including a combustion-tube 11, into which air and gas are introduced through pipes 12 13 from suitable compressors, each composed of low and high pressure cylinders 14 15 16 17 and intercoolers 18 19 20, being a valve controlled differentially by the pressures initial and terminal to it for maintaining a velocity of flow.

21 is the cooling-chamber containing a body of water 22, which is vaporized by the products of combustion passing downwardly around the lower end of the combustion-tube. In passing upwardly to the engine-pipe 23 the steam in the resultant mixed working fluid is superheated by contact with the outside of the combustion-tube 11.

24 represents a multi-expansion or compound engine of the steam-engine type, including high-pressure cylinder 25, intermediate receiver 26, and low-pressure cylinder 27, said engine being connected to drive the compressors 14 15 and 16 17. In passing through the engine the working fluid is first expanded in the high-pressure cylinder 25, doing work therein on the piston of said cylinder, from whence it is exhausted into the receiver 26 and from thence passes into the low-pressure cylinder 27, being further expanded in the latter and doing work on the low-pressure piston. From the low-pressure cylinder the fluid may be exhausted into the atmosphere or into a condenser.

Besides the efliciency gained as I have described it is to be noted that my cycle gives a diagram of considerable width as compared with its height, which means that with a given maximum temperature there is a much increased heat breadth, heat weight, or entropy to do work by dropping in stages to atmospheric pressure. It is this breadth of cycle, measured per cubic foot or per pound of working substance, 'which measures the specific capacity of the engine or the amount of power which it will develop for a given size or cost of engine. In this respect the Reeve cycle exhibits the advantages of the form of cycle of the ordinary steam-engineand embodies those capabilities inherent in the steamengine which have enabled it to succeed as a practicable motor and even in crude forms of construction.

While it may be alleged that the nature of the process of internal combustion under constant pressure, involving the constant action of air-compressors, forbids an engine operating on this cycle from assuming a par with the steam-engine in point of simplicity of construction, yet the features just referred to enable the cycle which I have described to compete successfully with the Otto cycle en,- gine, which, so far as I am aware, is the only other commercially successful type of internal-combustion motor, this cycles ability to compete being based upon considerations of mechanical adaptability, compactness, and reliability in addition to the thermodynamic considerations which I have already explained.

It will be understood that while I consider the water-pool as the best agency for quenching the products of combustion, the invention is not confined to such means of bringing together the water and hot gases, nor in other respects is it confined to the exact manner of procedure here furnished for purposes of illustration.

I claim 1. The method of developing heat energy by internal combustion and converting it into mechanical energy by expansion of a fluid medium which consists in burning fuel in a closed chamber, maintaining in said chamber the described highpressure, bringing the products of combustion into contact with a body of water while still under the said high pressure to reduce their temperature and to add thereto a medium containing latent heat, and expanding the resulting medium in a suitable motor in a plurality of successive stages to convert the heat energy thereof into mechanical energy.

2. 'The method of developing heat energy by internal combustion and converting it into mechanical energy by the expansion of a fluid medium which consists in compressing 7 a combustion fluid by successive stages into a closed chamber at the described high pressure, burning the fuel in said chamber while maintaining substantially said pressure, bringing the products of combustion into contact with a body of water while still under the said high pressure to reduce their temperature and to add thereto a medium containing latent heat, and expanding the resulting medium in a suitable motor.

3. The method of developing heat energy by internal combustion and converting it into mechanical energy by the expansion of a fluid medium which consists in compressing a combustion fluid by successive stages into a closed chamber at the described high pressure, burning the fuel in said chamber while maintaining substantially said pressure, bringing the products of combustion into contact with a body of water while still under the said high pressure to reduce their temperature and to add thereto a medium containing latent heat, and expanding the resaid high pressure to reduce their tempera ture and to add thereto a medium containing latent heat, superheating the steam in the re sulting medium, and expanding said medium in a suitable motor in a plurality of successive stages to convert the heat energy thereof into mechanical energy.

5. The method of developing heat energy by internal combustion and converting it into mechanical energy by the expansion of a fluid medium which consists in compressing a combustion fluid by successive stages into a closed chamber at the described high pressure, burning the fuel in said chamber while maintaining substantially said pressure, bringing I 5 the products of combustion into contact with a body of Water While still under the said high pressure to reduce their temperature and to add thereto a medium containing latent heat, superheating the steam in the resulting 20 medium, and expanding the resulting medium in a suitable motor.

Iii-testimony whereof I have affixed my signature in presence of two witnesses.

SIDNEY A. REEVE. WVitnesses:

E. M. BENTLEY, R. M. PIERSON. 

